Effect of a sodium hypochlorite mouthwash on plaque and clinical parameters of periodontal disease‐a systematic review

Abstract Objective The present study aimed to establish the efficacy of sodium hypochlorite mouthwash (NaOCl‐MW) compared with a control mouthwash on plaque and clinical parameters of periodontal disease. Methods MEDLINE‐PubMed, Embase and Cochrane‐CENTRAL databases were searched for clinical trials on patients with gingivitis or periodontitis that assessed the effect of NaOCl‐MW in comparison with a negative or positive control on plaque index (PI), gingival index (GI), and bleeding index (BI) scores and probing pocket depth (PPD). Data were extracted from the eligible studies. Results Seven eligible papers were retrieved, which together represented six clinical trials. The studies showed considerable heterogeneity regarding methodological and clinical aspects that did not permit a meta‐analysis. Two of the three studies in which NaOCl‐MW was compared with a negative control showed that NaOCl‐MW significantly reduced PI, GI and BI, and no effect was found on PPD. In three studies, NaOCl‐MW was assessed using chlorhexidine mouthwash (CHX‐MW) as a positive control; no difference was found for GI and BI. One of the three comparisons showed a statistically significant PI score favouring NaOCl‐MW. One study measured PPD and found it to be significant in favour of NaOCl‐MW. Conclusions Studies with a negative control group provided very weak quality evidence for a very small beneficial effect of NaOCl‐MW on PI, GI and BI scores. Studies with a positive control group provided very weak quality evidence that NaOCl‐MW had a similar effect as CHX‐MW on PI, GI and BI scores. The outcome for PPD was inconclusive.

lead to tooth loss, which has an adverse effect on chewing, speech, quality of life, and self-confidence and may have systemic inflammatory consequences. 3,4 To maintain a healthy periodontium or treat periodontal disease, dental plaque needs to be daily and meticulously removed.
Mechanical plaque removal with a manual or electric toothbrush is the first choice of oral hygiene device to reduce dental plaque. 3 Interproximal cleaning devices are also recommended as adjunct to toothbrushes. 5 However, there is substantial evidence that efficient mechanical plaque control is not achieved by most individuals of the general population. 6,7 Several reasons are proposed, including limited time of usage and limited use of interdental cleaning devices.
Therefore, chemical plaque control could be considered as a part of daily home care measures. 3,8 Adjunctive anti-microbial agents are available to consumers in the form of mouthwash and toothpaste/gel.
Chlorhexidine mouthwash (CHX-MW) is a regularly advised chemical plaque control product and is considered as a gold standard.
It has both bactericidal and bacteriostatic properties. There is a large body of evidence that supports the effectiveness of CHX-MW, showing that it can significantly improve parameters of plaque and gingivitis. 9,10 However, CHX also has some side effects such as stimulation of calculus formation, hypogeusia, burning sensation, hypersensitivity and extrinsic tooth staining from long-term use. 9 These side effects may have a negative effect on patient compliance in using this mouthwash. Therefore, dental care professionals commonly do not advise the use of CHX-MW for an extended period. 9,11,12 Sodium hypochlorite (NaOCl) has been used for various purposes around the world as a strong anti-microbial agent. It is used in hospitals, animal facilities and potable water supplies, and it serves as a food additive and bleaching agent. 13 In dentistry, it is employed, in concentrations of 1%-6%, as the favoured root canal irrigant for treating endodontic infections. 14,15 In water, NaOCl settles an equilibrium with Na + , OH − and hypochlorous acid (HOCl). HOCl is a weak acid that further dissociates into H + and hypochlorite ion (OCl − ).
HOCl has stronger anti-microbial abilities than OCl − . This can partly be explained by the fact that pathogenic microorganisms by nature have negatively charged cell walls. These cell walls can only be penetrated by neutrally charged HOCl and not by OCl − . 16,17 Hypochlorous acid is capable of penetrating the polysaccharide plaque matrix and oxidizing and disrupting the cell wall, cell membrane and various macromolecules of microorganisms, such as proteins, nucleotides and lipids. 18 NaOCl is naturally produced in activated inflammatory cells such as neutrophils and macrophages and plays a crucial anti-microbial role in the innate immune system. 19 Thus, it does not evoke allergic reactions; is not a carcinogen, mutagen, teratogen, or cytotox; and has a century-long safety record. 20 Histologically, no damage was observed to periodontal connective tissues after applying 6% NaOCl subgingivally. 21 It also does not increase the risk of resistance development because it attacks multiple components of infectious agents. In 1984, The American Dental Association Council on Dental Therapeutics designated 0.1% NaOCl as a mild antiseptic mouthrinse, and its suggested use is direct application on the mucous membrane. 22 NaOCl can be used as a mouthwash as it has excellent antimicrobial properties and is a safe and low-cost antiseptic agent.
Sodium hypochlorite is available in most homes as a household bleach. It has been suggested that patients could dilute inexpensive basic household bleach to reach the recommended concentration. 23,24 Several studies have shown that it has anti-microbial activity against the dental plaque microflora and can reduce gingivitis. [25][26][27] However, there are other scientific studies that do not support this proposition. 28 Therefore, at present, the results published regarding the effectiveness of NaOCl remain inconclusive.
The purpose of this systematic review was to gather and synthesize all the available scientific literature to investigate and compare the efficacy of NaOCl mouthwash (NaOCl-MW) with that of control mouthwashes on plaque scores and clinical parameters related to periodontal disease.

| MATERIAL AND ME THODS
The preparation and presentation of this systematic review are in accordance with the Cochrane Handbook for Systematic Reviews of Interventions 29 and the guidelines of Transparent Reporting of Systematic Reviews and Meta-Analyses (PRISMA). 30 A protocol was developed a priori following an initial discussion among the research team members. 31 This systematic review was registered beforehand at ACTA ETC (protocol number 202093) and PROSPERO (protocol number 236831).

| Focus question (PICO)
In patients with gingivitis or periodontitis, what is the effect of rinsing with NaOCl-MW compared with a control mouthwash on plaque scores and clinical parameters related to periodontal disease?

| Search strategy
To retrieve studies concerning the effect of NaOCl-MW, a struc-  Table 1 provides details regarding the search terms used. There were no restrictions on publication date.

| Screening and selection
For all studies obtained from the search, the title and abstract (when available) were judged independently by two reviewers (AMS and DES) using the Rayyan 32 web application. Studies that potentially fulfilled the inclusion criteria for full-text reading or for which the title and abstract provided inadequate information to make a clear assessment were selected. After reading the full texts, the studies were categorized as 'definitely eligible', 'definitely not eligible' or 'questionable'. Disagreements concerning eligibility were resolved by consensus or-if disagreement persisted-by arbitration by a third reviewer (GAW). The papers that fulfilled all of the inclusion criteria were processed for data extraction. Attempts were made to contact the authors of the included publications to request additional data or information if the paper was unclear.
The inclusion criteria were as follows: 1. Randomized controlled trials (RCTs) or controlled clinical trials

| Assessment of heterogeneity
The following factors were considered to determine the heterogeneity of the outcomes of the different studies: study design, evaluation period, subject characteristics, control groups, NaOCl concentration, mouthwash brand and rinsing procedure.

| Methodological quality assessment
The potential risk of bias of the studies included in this review was estimated independently by two reviewers (AMS and DES) using the checklist for RCTs presented in Appendix S1 as proposed by Van der Weijden et al. (2009). 34 If there was a disagreement between two reviewers, a consensus was achieved through discussion. If there was no consensus after the discussion, the opinion of a third reviewer (GAW) was decisive. In brief, when positive scores were assigned to defined inclusion/exclusion criteria, random allocation, balanced experimental groups, blinding of the patient to the product, blinding of the examiner, identical treatment between groups (except for intervention) and reporting of followup, the study was classified as having a low risk of bias. When the study fulfilled only six of these seven criteria, it was considered to have a moderate risk of bias. If more than one of these seven criteria remained unfulfilled, the article was considered to have a high risk of bias.

| Data extraction and analysis
For all the included studies, data extraction was performed by two independent reviewers (AMS and DES) using a custom-designed data extraction form. Data recorded were based directly on the focus of the research question and also included details of the study population, intervention, comparison, outcome and study characteristics. Means and standard deviations were extracted if available. A consensus was achieved through discussion if there was a disagreement between two reviewers. Any persisting disagreements were resolved by discussion with a third reviewer (GAW). To obtain a summary of the data, a descriptive data presentation was used for all the studies. 35 It was decided in advance to categorize the NaOCl-MW studies into either negative control group studies or positive (CHX or EO-MW) control group studies. 33 The PI, GI, and BI scores and PPD measurements were taken into account.

| Grading the body of evidence
The Grading of Recommendation, Assessment, Development and Evaluation (GRADE) system was used to rank the evidence emerging from this review. [36][37][38] Two reviewers (AMH and DES) rated the quality of the evidence and the strength and direction of the recommendation according to the strength of the following aspects: risk of bias, consistency of results, directness of evidence, precision, reporting bias and magnitude of effect. Any disagreement between the two reviewers (AMH and DES) was resolved by additional discussion with GAW.  for which the full texts were obtained and read in detail. All seven papers were found to be eligible. Manually searching the reference lists of these papers did not yield additional publications. The seven  with a positive control.

| Assessment of heterogeneity
The six clinical trials showed heterogeneity with respect to study design, evaluation period, participants, control groups, mouthwash concentration and brand, rinsing procedure, and assessment parameters. Information regarding the study characteristics is presented in Table 2.

| Study design and participant characteristics
Five of the selected comparisons were parallel-design RCTs (I, 26   VI 41 ), full-mouth supra-and subgingival ultrasonic treatment was provided before the participants started using the mouthwash. In comparison V, 39,40 participants received subgingival irrigation with either 0.25% NaOCl or water at baseline and after 2 weeks in addition to self-performed mouth rinsing.

| NaOCl concentrations
The NaOCl concentration in the mouthwashes used differed across the studies. A concentration of 0.25% was used in comparisons III 27 and V, 39,40 a concentration of 0.05% in studies I 26 and VI, 41 a concentration of 0.1% in study II 28 and a concentration of 0.5% in study IV. 25 In studies III, 27

| Rinsing regimen
The rinsing procedure was set at twice daily for 60 s in studies I 26 and IV, 25 twice daily for 30 s in studies II 28 and III, 27 and twice per week for 30 s in comparison V. 39,40 In study VI, 41 25 were asked not to eat or drink for 30 min after mouth rinsing, and those in study V 39,40 were asked not to rinse with water for at least 10 min.

| Methodological quality assessment
The potential risk of bias was estimated on the basis of methodological quality aspects of the included papers using the checklist presented in Appendix S1. Based on the summary of the proposed criteria, the estimated risk of bias was low for comparison II, 28

| Study outcomes
The results reported by the included studies for PI, GI, BI and PPD are presented in Appendix S2. A meta-analysis could not be performed owing to missing and irretrievable data and a complex diversity of study design and indices used to measure the outcome parameters. Accordingly, only a descriptive analysis was performed, which is presented in Table 3.

| Comparisons with a negative control
Two of the three comparisons that used water as a negative control (I, 26

| Comparisons with a positive control
In studies III, 27 IV 25 and VI, 41 which used CHX-MW as a positive control, no statistically significant difference was found for the parameters GI and BI. One of the three studies (III 27 ) showed a statistically significant PI score in favour of NaOCl-MW, indicating that NaOCl-MW is more effective than CHX-MW. One study (VI 41 ) measured PPD and found it to be statistically significant in favour of NaOCl-MW. Table 4 presents a summary of the various aspects that were used to rate the quality of the evidence and to assess the strength and

| Analysis
Owing to the heterogeneity of the indices used in the included studies and different study designs, it was impossible to combine the outcomes for a meta-analysis. Instead, vote counting was used to synthesize the results of the selected studies. The Cochrane Handbook advises to limit vote counting to answer a simple question: Is there any evidence of an effect? 29 The study results were differentiated as non-significant, significantly negative and significantly positive. With this classification, it was possible to combine the statistical analyses of the individual studies into an overall summary. 49 The vote counting method, however, considers each study and each vote as equal and neither presents an estimate of the effect size of an intervention nor evaluates the precision. 50 Hedges and Olkin affirm that vote counting is an appropriate method when only studies that show positive significant effect are considered. 51 The data extracted for the present review were assessed accordingly. Positive outcomes of NaOCl-MW on plaque scores and other parameters related to periodontal health were regarded in consideration of the estimate of the overall effect.

TA B L E 4 Summary of findings table
based on the quality and body of evidence on the estimated evidence profile and appraisal of the strength of the recommendation regarding the efficacy of NaOCl-MW as compared to water or CHX-MW (gold standard)

| Outcome
The fact that one of the three comparisons with a negative control (II 28

| Side effects
The One side effect that was not addressed in any of the included studies was the bleaching effect of the rinsing solution if spilled, for instance, on clothing.

| Hypochlorous acid
In water, NaOCl settles at an equilibrium with the strong active anti-

| Safety of NaOCl
The thought of using household bleach as a mouthwash may be an issue of concern for some patients who consider it harmful. The ADA approval of an over-the-counter NaOCl-MW would likely reassure patients regarding its safety and efficacy. However, it is questionable whether such a product is attractive from a commercial perspective as people could use household bleach in a diluted form. Household bleach contains (according to manufacturers) water, NaOCl, sodium chloride (stabilizes formula), sodium carbonate (maintains alkalinity), sodium chlorate (is a process by-product), sodium hydroxide (pHadjuster) and sodium polyacrylate (assists in cleaning).. 56,57 Two trials included in this review used Clorox in a diluted form and did not find any harmful side effects. 27,39,40 Moreover, the ADA has proposed 0.1% NaOCl as a topical antiseptic for irrigation of wounds and as a mouthwash. 22 Furthermore, Kalkwarf et al. (1982) 21

| Limitations
This review has certain limitations. Specifically, the observed heterogeneity with respect to the study design and risk of bias makes it challenging to make a recommendation that is more than an expert opinion. Moreover, the English language criterion may have introduced a language bias. However, over the years, the extent and effects of such a possible bias have diminished because of the shift towards publication in the English language. 59

| Recommendation for further research
A meta-analysis could not be performed on the studies that were included in this systematic review. To assist dental care professionals in providing evidence-based recommendations for an NaOCl-containing anti-microbial mouthwash, there is a need of studies more homogeneous in terms of study design, NaOCl concentration, periodontal conditions of the patients, rinsing procedure, and indices used to measure plaque and periodontal parameters. In the future, this would allow for a meta-analysis that takes the data one step further than the present descriptive analysis. Additionally, it appears of interest to evaluate a dose-response effect of different NaOCl concentrations in a single RCT in which the side effects, and thus patient comfort, are also assessed more precisely. Two included clinical trials used household bleach as the source of NaOCl. As using household bleach could be an issue of concern, it would be interesting to investigate the effects of the other main ingredients of household bleach in low concentrations on oral soft and hard tissues. This information would assure people about the safety of using household bleach; it would be valuable especially for low-income individuals as they are mostly at elevated risk for periodontal diseases 60,61 because they lack the education on personal oral hygiene and are unable to afford oral care products of recognized brands. 62 Therefore, there is a need to implement efficacious and low-cost dental care products. NaOCl, which is widely available as household bleach, could be a low-cost alternative. 24,60

| CON CLUS ION
Studies with a negative control group provided very weak quality evidence for a very small beneficial effect of NaOCl-MW on PI, GI and BI scores. Studies with a positive control group provided very weak quality evidence that NaOCl-MW had a similar effect as CHX-MW on PI, GI and BI scores. The outcome for PPD was inconclusive.

| Scientific rationale for the study
Most individuals cannot achieve efficient mechanical plaque control. Thus, adjunctive use of anti-microbial agents may be required.
NaOCl has been proposed as an inexpensive mouthwash for longterm use.

| Principal findings
Compared with a negative control, NaOCl-MW showed a significant effect on PI, GI and BI scores. Summary data of the comparisons with CHX-MW as a positive control suggested no significant difference.

| Practical implications
There is very weak quality evidence that household bleach in a diluted form can be prescribed as adjunct to mechanical cleaning to prevent or treat plaque and gingivitis.

ACK N OWLED G EM ENTS
We would like to thank our colleagues who provided us with ad-

AUTH O R CO NTR I B UTI O N S
AMH contributed to design, search and selection, analysis and interpretation, and drafted the manuscript. DES contributed to conception and design, search and selection, analysis and interpretation, and critically revised the manuscript. GAW contributed to conception and design, analysis and interpretation, and critically revised the manuscript. All authors gave final approval and agreed to be accountable for all aspects of work ensuring integrity and accuracy.

E TH I C A L A PPROVA L
Ethical approval was not required, and the protocol was registered at ACTA ETC (protocol number 202093).